Joint Contact Forces with Changes in Running Stride Length and Midsole Stiffness Abstract The purpose of this study was to determine if lower extremity joint loading was influenced by stride length or shoe midsole cushioning. Ten subjects completed 10 trials of overground running at an average speed of 4.43 m/s in each of three conditions: normal running, running with a stride length (SL) reduced by 10% of normal, and running with a cushioned midsole stiffness (i.e., mechanical impact reduction of 13.7–10.9 g). Reaction forces calculated from inverse dynamics were summed with muscle forces estimated from a musculoskeletal model using static optimization to obtain joint contact forces at the hip, knee and ankle joints. Peak components of the contact forces [axial, anterior–posterior, and medial–lateral (ML)] were examined using parametric statistics (α = 0.05). Reducing stride length resulted in significant decreases in absolute peak ankle contact forces in the axial direction (normal: − 14.5 ± 1.5 BW; reduced SL: − 14.0 ± 1.6 BW) and the ML direction (normal: 0.67 ± 0.23 BW; reduced SL: 0.61 ± 0.21 BW). Reducing stride length also reduced the peak absolute axial forces at the knee (normal: − 10.6 ± 1.3 BW; reduced SL: − 9.8 ± 1.2 BW) and the hip (normal: − 7.26 ± 2.24 BW; reduced SL: − 6.75 ± 2.10 BW). The cushioned shoe did not statistically reduce the peak absolute contact forces from the normal stride condition at any of the joints. Post hoc stress analysis suggested that the observed changes in anterior hip force would increase stress more than any of the other statistically significant results. Reductions in stride length appear to decrease some joint contact variables but cushioning in the heel region of the shoe does not.

Exercise and Ion-Channel Remodeling in Vascular Smooth Muscle During Hypertension: Therapeutic Implications Abstract Myogenic contraction of vascular smooth muscle cells (VSMCs) in resistance arteries and arterioles plays a critical role in regulating peripheral resistance. Ion channels expressed in VSMCs control ion influx or efflux from the plasma membrane and endoplasmic reticulum to regulate membrane potential, which contributes to the regulation of vascular tone. With the depolarization of VSMC membranes, an elevation of intracellular calcium ion (Ca2+) concentration is mediated by voltage-gated Ca2+ channels and can trigger a vasoconstrictive response. In addition, potassium ion (K+) efflux through K+ channels can hyperpolarize VSMCs, resulting in vasodilation. However, in the pathophysiological progression of diseases such as hypertension, VSMCs undergo a wide range of pathological changes, among them is “electrical remodeling”, which refers to changes in ion channels. Under physiological or pathological conditions, exercise has a profound impact on the human body, and ion channels are an essential target of the beneficial adaptive responses. This review provides insight on the physiological function of ion channels in VSMCs, including CaV1.2 channels, voltage-gated K+ channels, large-conductance Ca2+-activated K+ channels, and inward-rectifier K+ channels, and the changes of these ion channels during hypertension. Focus is given to the effects of exercise on these ion channels and its implications in disease treatment.

Tensegrity: A Novel Conceptual Framework for Rehabilitation of Functional Deficits for Breast Cancer Survivors Abstract The current approach to breast cancer rehabilitation is currently narrowly focused on addressing resultant problems such as lymphedema or shoulder pain. Referrals to rehabilitation are reactive responses to these problems. Taking a step back and looking at the breast cancer intervention in totality, it becomes apparent that steps could be taken to minimize or actually prevent some of the ensuing functional problems by proactively treating a breast cancer survivor. Rather than waiting for problems to arise, immediately post-intervention or ideally pre-intervention and throughout intervention referral of an individual to rehabilitation could provide a supportive role in the functional progression of the patient. Furthermore, while most orthopedic rehabilitation focuses on the function of a particular joint, with the extensive impact of the breast cancer treatments on the soft tissue of the body without any specific intervention at a joint, it is imperative that we begin to shift our rehabilitation approach to focusing on the alterations of the soft tissue prior to addressing any functional limitations in the joints, with the most common victim being the shoulder joint. This novel approach to breast cancer rehabilitation suggests initially addressing soft tissue limitations. As these limitations begin to resolve as optimally as possible, secondary consideration is then given to functional limitations of a joint such as the shoulder joint.

Methodological Considerations Which Could Improve Spinal Cord Injury Research Abstract Advances in spinal cord injury-based research in the last 50 years have resulted in significant improvements to therapy options. However, the efficacy of such research could be further enhanced if threats to internal and external validity were addressed. To provide perspective, a sample topic was identified: the effects of acute and chronic exercise on clinical and sub-clinical markers of cardiovascular health. The intention was not a systematic review, nor a critique of exercise-based research, but rather a means to generate further discussion. Thirty-one articles were identified, and four common issues were found relating to: (1) sampling; (2) study design; (3) control group; and (4) clinical inference. These concerns were largely attributed to insufficient resources, and challenges associated with recruiting individuals with spinal cord injury. Overcoming these challenges will be difficult, but some opportunities include: (1) implementing multi-center trials; (2) sampling from subject groups appropriate to the research question; (3) including an appropriate control group; and (4) clearly defining clinical inference. These opportunities are not always feasible, and some easier to implement than others. However, addressing these concerns may assist in progressing spinal cord injury-based research, thereby helping to ensure steady advancement of therapy options for persons with spinal cord injury.

Exercise Training for the Elderly: Inflammaging and the Central Role for HSP70 Abstract Inflammation is a common feature of aging tissues, being involved in most, if not all, age-related diseases. The origin of a low-grade inflammation state in aging (inflammaging) is multifactorial and may involve changes in body composition, immunosenescence, autophagy, microbiota modification and loss of proteostasis. The heat shock response pathway (HSR, and HSP70 expression) plays an important role as a mechanism of resolution of inflammation and proteostasis control. In this review, we sought to discuss the mechanisms that may lead to inflammaging, and the importance of the HSP70 in this process. Besides, we also discuss how physical exercise, particularly resistance training, can improve the HSR and the inflammatory balance of elderly people.

Effect of the Resistance Exercise on Elementary School Students’ Physical Fitness Abstract Background Physical activity programs using components of resistance have the potential to improve health in school children. The purpose of this study was to examine the effect of a school-based resistance exercise program on physical fitness in elementary school students. Methods The sample was 256 children (mean age = 8.3 ± 2.5 years; 119 girls) from kindergarten to 5th grade. Participants performed a 10-min resistance exercise 2–3 times in each school day. Physical fitness outcomes were assessed using President’s Physical Fitness Challenge test. Measures were collected at baseline and at a 6-month post-test time point. A 2 × 2 doubly MANOVA was employed to examine the effect of sex and time. Results The multivariate model was statistically significant with a main time effect (Wilks’ λ = 0.19, F = 290.9, P < 0.001). Follow-univariate tests found significant differences between time-points on flex arm hang (P = 0.033), shuttle run (P < 0.001), and 1-mile run/walk times (P < 0.001). Conclusions A 6-month resistance exercise program improved upper body strength and cardiorespiratory endurance in elementary school aged children. The use of resistance exercise intervention during school day can be effectively used to promote physical fitness and ultimately improve the health of children.

The Sensitivity of the Critical Resistance Model to Detect Sex-Related Differences in Fatigue During Submaximal Muscular Contractions Abstract Purpose Critical resistance (CR) is a fatigue threshold that, theoretically, estimates the highest sustainable resistance for repeated skeletal muscle contractions. Men are typically more susceptible to fatigue than women during sustained muscular contractions. Therefore, the purpose of this study was to compare the CR between men and women to determine the sensitivity of the CR model to detect sex-related differences in fatigue at submaximal intensities. Methods Ten men and 10 women completed one-repetition maximum (1RM) testing for the deadlift and repetitions to failure at 50%, 60%, 70%, and 80% of 1RM for the determination of CR. Repetitions to failure were then performed at the estimated CR. Results The men had a greater absolute 1RM (168 ± 27 kg vs. 115 ± 11 kg) and CR (62 ± 14 kg vs. 48 ± 6 kg), but a lower relative CR (percent of 1RM; 37 ± 6% vs. 41 ± 2%) and completed fewer repetitions at CR (45 ± 14 repetitions vs. 58 ± 12 repetitions) compared to the women. Conclusions The CR model was sensitive to detect sex-related differences in fatiguing muscular contractions of the deadlift. In addition, the men were more susceptible to fatigue than the women during performance of submaximal muscular contractions at CR, which may be related to sex-dependent physiological responses during fatiguing muscular contractions.

Career Performance Progressions of Junior and Senior Elite Track and Field Athletes Abstract Purpose To compare and assess differences in the career performance progressions of elite junior and Olympic track and field athletes. Methods Annual best performances from top 8 men and women (e.g. finalists) in track and field events at the 2000 World Junior Championships (junior cohort) and the 2000 Olympic Games (Olympic cohort) were examined. Annual bests of these finalists were tracked each year from select groups: sprints (100 m, 200 m), distance (1500 m, 5000 m), jumps (long jump, high jump), throws (discus, shot put). Age of best lifetime performance, age of final posted performance, and improvement from junior-age best to lifetime best performance were compared between groups. Results Olympic finalists achieved lifetime best performances at later ages than junior finalists [26.0 ± 4.0 years vs. 21.1 ± 3.5 years; age difference 90% CI (3.7–5.2 years), P < 0.001], and this significant age difference between cohorts was found within all four groups. Olympic finalists improved from under-20 best to lifetime best more so than junior finalists [6.1 ± 4.8% vs. 2.5 ± 2.3%; Age difference 90% CI (2.5–4.8%), P < 0.001]. Of 130 junior finalists, 54 did not improve after age 19, while 19 of 128 Olympic finalists posted no improvement after age 19. Conclusion The data suggest that these two populations have different career performance progressions and challenge the notion that achieving elite success as a junior athlete is a prerequisite for the same success at the senior level.

Correlations Between Myoelectric and Hemodynamic Parameters Changes in Biceps Brachii During Sustained Isometric Contraction in Healthy Elderly Abstract Purpose The purpose of the present study was to evaluate the Pearson correlations between hemodynamic parameters obtained with near infrared spectroscopy (NIRS), namely total hemoglobin (tHb) and tissue oxygen index (TOI %), as indicators of blood flow and oxygen extraction, and myoelectric parameters obtained with surface multichannel electromyography (sEMG), namely fractal dimension (FD) and conduction velocity (CV) slopes, as descriptors of central and peripheral fatigue, during sustained high level isometric contractions at 60% maximal voluntary contraction (MVC), in elderly subjects. Methods Ten recreationally healthy elderly subjects (age 67.7 ± 4.6 years), 5 males and 5 females, performed one isometric contraction of the elbow flexors at 120° joint angle at 60% of MVC until exhaustion in two subsequent trials 1 week apart, one for the sEMG and the other one for NIRS recordings from the biceps brachii. Results A negative strong Pearson’s correlation between TOI % slope in the functional hyperemic phase (HP) of contraction and a positive correlation between the slope of TOI % recorded during the ischemic phase (IP) and the CV slope were found (r = − 0.76, P < 0.05; r = 0.91, P < 0.01, respectively). A negative strong correlation between tHb IP slope and tHb HP slope and TOI % IP slope and TOI % HP slope (r = − 0.78, P < 0.01; r = − 0.78, P < 0.01, respectively) were also found. No correlation was found between FD slope and hemodynamic parameters (FD slope vs. HP tHb slope, r = − 0.19; FD slope vs. IP tHb slope, r = 0.16; FD slope vs. HP TOI % slope, r = 0.19; FD slope vs. IP TOI % slope, r = 0.27). Conclusion In aged individuals, CV slope correlated with muscle O2 desaturation (TOI %) rather than reduced muscle blood flow (tHb) in the ischemic phase of isometric contraction to exhaustion. No correlations were found between myoelectric manifestations of central fatigue (FD slope) and data obtained by NIRS.

Differences in Kinetics, Kinematics and Muscle Activation Strategies in Male and Female Team Sport Athletes During Unanticipated Sidestepping Abstract Purpose The purpose of this study was to compare kinetics, kinematics and muscle activation strategies between male and female collegiate level athletes during unanticipated sidestepping tasks to further the understanding of sex-specific differences in injury incidence and their potential influence on ACL injury risk. Methods Three-dimensional kinematics, ground reaction forces and surface electromyography of eight lower limb muscles were recorded during unanticipated sidestepping in 20 male soccer and 17 female field hockey National Collegiate Athletics Association Division 1 athletes. Trunk, hip and knee kinematics, knee joint moments, total muscle activation (TMA: knee, gluteal, quadriceps, hamstrings and gastrocnemii) and directed co-contraction ratios (DCCR) were compared between groups with two-sample t tests. Results No sex differences were observed for peak frontal and transverse plane knee moments (P > 0.05), however males had 10% greater knee flexion moments (P = 0.047). Females had lower hip flexion and abduction and greater hip internal rotation angles than males likely concomitant with the 30% reduction in gluteal TMA (P < 0.05). Females had lower quadriceps TMA during pre-contact and weight acceptance and higher hamstrings TMA during weight acceptance (P < 0.05). Group averages for DCCR were not representative of individual patterns, where the majority of males were quadriceps dominant compared with females. Conclusions Female and male team sport athletes display similar frontal and transverse plane knee moments, however their ability to support/counter the load applied (i.e., muscle activations strategies) to the knee joint differed.